In situ monitoring and analysis of the photocatalytic degradation process and mechanism on recyclable Au NPs-TiO2 NTs substrate using surface-enhanced Raman scattering

• Photocatalysis, SERS activity and recyclability of Au NPs-TiO2 NTs are characterized.
• In situ monitored the photodegradation of methylene blue (MB) by applying SERS.
• Analysis of time course SERS spectra interpreted the MB degradation pathway.
• The kinetics of photodegradation of MB on the substrate/air interface are analyzed.
• Mapping of temporal distribution of methylene blue on substrate are achieved.

An in situ method that is able to quickly and accurately detect not only the photocatalytic degradation process but also the molecular structure information of intermediates is critical to analyzing the degradation mechanism of organic contaminants. This work successfully applied Raman microspectroscopy to in situ detect and monitor the photocatalytic degradation process of methylene blue (MB) on a recyclable substrate (gold nanoparticles dispersed TiO2 nanotube arrays, noted as Au NPs-TiO2 NTs) that exhibits multifunctionalities including photocatalysis activity and surface-enhanced Raman scattering (SERS) effect. In addition, by analyzing time course SERS spectra during the photocatalytic degradation process, the intermediates produced in the proposed photocatalytic degradation pathway were identified and the kinetics of photocatalytic degradation of MB on the Au NPs-TiO2 NTs/air interface were interpreted. This work demonstrated the potential of using these recyclable, highly photocatalytical and SERS active nanostructures as a platform to analyze the photocatalytic degradation mechanism and kinetics of other environmental pollutants.

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